Thank you for these additional images.

The second new picture shows the head to be bulge-formed (one-piece). It is made by Agrati and is a pattern called "SPORT" which has the part nr. 000.8056. The seat lug bare, without any form of binder, is also Agrati "SPORT" series and is item nr. 023.8059. Fork ends, while not shown, are likely Agrati nr. 000.8010. Bottom bracket shell looks to be Agrati "SPORT" pattern as well but is not depicted in the catalogue I have. The "SPORT" framebuilding set as a group is item nr. 000.8050/U.

Seat binder arrangement does not make frame a Bianchi. Other manufacturers used this arrangement as well.

Bottom bracket shell will have a width of 70mm and be threaded 36mm X 24TPI.

One variable not as yet mentioned which may potentially advance an identification is serial number format. You mentioned it is located on lower head. If able to post a photo its format may tweak a reader's memory. As to the suggestion of Bianchi-ness the forum has a well established discussion thread on the subject of Bianchi serial numbers you may wish to explore:

http://www.bikeforums.net/classic-vi...ification.html

Through the years the company placed their serials all over the frame. Some spots have included front of seat lug, back of seat lug, upper head lug, lower head lug, bottom bracket shell, dropout, head tube itself, etc.